Polyamide resins possess excellent mechanical properties, moldability, and chemical resistance and have therefore been used in automotive parts, electric/electronic components, mechanical components, and many other applications. Articles made from polyamide resins possess extremely desirable physical properties. However, in certain applications, it is desirable that polyamide resin compositions be flame retardant and meet the UL-94 standard for a high degree of flame retardance. This requirement has promoted research into a variety of methods for imparting flame retardance to polyamide resins. A common method of imparting flame retardance to thermoplastic resin compositions involves incorporating a halogenated organic compound such as brominated polystyrene as a flame retardant along with an antimony compound that acts as a synergist for the flame retardant. However, the use of halogenated flame retardants has certain drawbacks in that these materials tend to decompose or degrade at the temperatures used to mold polyamide compositions. The degradation products can corrode the barrels of compounding extruders, the surfaces of molding machines, and other equipment halogenated flame retardants come in contact with at elevated temperatures. The degradation products of halogenated flame retardants can also result in molded articles that have poor surface appearance.
The use of non-halogenated flame retardants such as phosphate or phosphinate compounds with triazine derivatives has been proposed in WO 96/09344 but these flame retardants are unstable at high temperatures and can decompose or degrade during molding, leading to detrimental effects on the electrical properties of a compounded polyamide resin composition containing these flame retardants, especially under conditions of high humidity.
Thus, effective non-halogenated flame retardants that have good heat stability and that do not have a detrimental effect upon a resin's properties, in particular electrical properties, are desirable. U.S. Pat. No. 5,773,556 discloses compositions comprising polyamide and phosphinate or diphosphinate. U.S. Pat. No. 6,255,371, however, discloses compositions comprising polymers such as polyamide or polyester, with a flame retardant comprising phosphinate or diphosphinate and melamine derivatives such as condensation products of melamine and/or reaction products of melamine with phosphoric acid and/or reaction products of condensation products of melamine with phosphoric acid and/or a mixture of these. Phosphinates or diphosphinates without melamine derivatives are shown to be ineffective for flame retarding glass-reinforced aliphatic polyamides.
Based on the foregoing discussion, an object of the present invention is to provide a flame resistant polyamide resin composition capable of yielding articles that possess excellent flame retardance and good physical properties and good electrical insulation properties even under conditions of high humidity. A further object of the present invention is to provide shaped structures and parts that meet UL-94 standards for flame retardancy for use in electrical and electronic parts that require good electrical insulation properties. A feature of the present flame resistant polyamide resin compositions is their good heat stability in molding and attendant excellent moldability. An advantage of the present compositions is their notable mechanical properties. These and other objects, features and advantages of the present invention will become better understood upon having reference to the following description of the invention.